arm/dts: Add support for AM335x BeagleBone

Add AM335X BeagleBone device tree source (am335x-evm.dts) file
to use the am33xx.dtsi SoC file, along with the memory node
information.

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Reviewed-by: Vaibhav Hiremath <hvaibhav@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>